(1) Technical Field
The present invention is related to the field of augmented reality, and more particularly to objects (fiducials) used to enhance the capabilities of augmented reality systems by providing location information and additional information regarding the objects.
(2) Discussion
Registration of virtual objects to real world objects is currently one of the most difficult challenges in building effective augmented reality systems. Accurate head tracking is a key part of this problem. Video see-through augmented reality systems have been demonstrated that use a video-based tracking system to track the location, in the video, of fiducial objects of known position and use these tracker measurements to estimate head orientation and location of the user. One drawback with these systems is that the location and appearance of the fiducials must be known in advance. This limits the use of fiducial-based tracking in actual working environments.
Two examples of fiducial use with augmented reality systems are disclosed in U.S. Pat. No. 6,064,749 to Hirota et al. and U.S. Pat. No. 5,926,568 to Chaney et al. U.S. Pat. No. 6,064,749 discloses a system in which landmarks are found in input image sequences and are used as fiducials to track the camera position and orientation. However, using landmarks requires knowledge of the landmark locations. Landmark locations serve as “passive” fiducials in the sense that they do not actively provide information to the augmented reality system. Rather, their location is already known and their world space positions are precisely calibrated in the system. U.S. Pat. No. 5,926,568 is similar in the sense that it uses known landmarks, but it provides an image-based object matching technique that uses passive fiducials.
Other examples of fiducial uses with augmented reality systems are discussed in the literature. The references provided below provide a combination of patents and articles that can assist the reader in obtaining a thorough overview of the current state of the art. A few examples of systems for which references are provided include that by Kangas et al. wherein a system is described in which real objects transmit code and data via a wireless communication link. The information passed is primarily for the purpose of explaining and facilitating the use of the objects.
Starner et al. describe a system in which visual tags are used on active objects to identify, to the augmented reality system, the room in which a user resides. The user location is determined by a priori knowledge of the location of objects.
A video see-through system in which passive machine-readable tags (e.g. barcodes) are read by the augmented reality system is presented in Rekimoto. No attempt is made, however, to use the data for head tracking, and the tags themselves are not active.
Want et al. describe a system in which the user carries an active infrared device into a room. In the room, sensors detect the emanations, compute the user's location, and then relay the information to the user. The system is not intended to track the user's orientation, and there is no mention of an augmented reality application for this system.
Although fiducial objects have been used in varying capacities with augmented reality systems, none of the uses contemplate the use of fiducial objects in an active manner such that they can be discovered and used as fiducials by a video-based tracker in an augmented reality system. Thus, a need exists in the art for a type of fiducial that incorporates an object (fiducial) with an attached or embedded computer system that uses a wireless communication subsystem to broadcast geospatial location, geometry, appearance, and other data to the augmented reality system for use by the video-based tracker. Thus, it is desirable to provide a computer system for providing location-registered patterns that incorporate information regarding objects in an area.
The following references are provided to assist the reader in gaining more knowledge regarding the state of the art in this technical area.